That tip on my site about the trs outputs only applies to the original 1604, not the 1604VLZ. If you've got the VLZ version and have phase problems, it's something else, either cables or something at your multitrack source.

Check your cables for polarity. Today's standard is pin-2 hot but there's lots of older gear out there that was pin-3 hot.

Also, are you sure it's not a mic placement problem? It's often pretty hard to hear a wiring phase problem, maybe instead it's due to mic positioning.